Study On Resistance To Sulfate Attack On Cement Based Composite Material Containing Mineral Additive

The production of traditional Portland cement consumes a lot of resources and energy and causes severe pollution, and its properties are not able to meet higher and higher requirements asked for modern constructions. To resolve the problems above of Portland cement, it is a basic and important approach to develop a kind of high performance Portland cement containing high-volume mineral additive. Thus study on resistance to sulfate attack on cement based composite material containing mineral additive was done here in order to guide the project of high performance cement and the main results are as follows:Firstly, based on the test comparison of different test methods of sulfate attack, it is suitable for identifying and evaluating the ability of cement based composite material containing mineral additive to resist sulfate attack with concrete prism (40mm×40mm × 160mm) whose W/B ratio is no less than 0.4. Test results are figured out with strength resistant coefficients (kp and kc). This test method can help us get hold of a trusty test result in an effective test period.Secondly, fly ash can improve the resistance to Na2SO4 attack on cement based composite material, while both ground blast furnace slag and coal gangue do contrarily. There is a linear relationship between the resistance to Na2SO4 attack on cement based composite material and the content of fly ash, ground blast furnace slag and coal gangue. The active effect of fly ash has nothing to do with the content of C3S and C2S in clinker, but the negative effect of ground blast furnace slag and coal gangue relates to them and is larger to the clinker with more C3S content. When both ground blast furnace slag and coal gangue are used with fly ash together, the negative effect falls. The effects above of mineral additives are a collective result of decreasing Ca(OH)2 content, improving structure of cement paste and producing more AFt crystal from more Al3+ solution of mineral additive by pozzuolanic reaction.Thirdly, there is a critical content for fly ash, ground blast furnace slag and coal gangue to have an effect on the resistance to MgSO4 attack on cement based composite material. When the content of mineral additives is less than their critical, mineraladditives can improve the resistance to MgSO4 attack on cement based composite material, or they decrease the resistance to MgSO4 attack, and the law follows a two-order multinomial function. This effect of mineral additives relates to the content of C3S and C2S in clinker and is less to the clinker with more C3S content. The effect above is also a collective result of decreasing Ca(OH)2 and Mg(OH)2 contents and improving structure of cement paste by pozzuolanic reaction.Fourthly, under the circumstances at 0 to 10℃ in temperature, sulfate attack damage for Portland-limestone cement based composite material results from another byproduct of sulfate attack-thaumasite. This type of sulfate attack damage can be suppressed by fly ash, while it is accelerated by coal gangue.Fifthly, when cement based composite materials are subjected to the action of both the sulfate attack and external flexural stress, the deterioration of the specimens is greatly aec(?)lorated compared to that subjected to the single action of the sulfate attack. The higher the stress level reaches, the more quickly the specimens deteriorate. Cement based composite material containing fly ash and the clinker with high C3S content has a better resistance to sulfate attack, while that containing coal gangue decreases the resistance to sulfate attack.Sixthly, when cement based composite materials are subjected to the action of both the sulfate attack and freezing-thawing cycles, the deterioration of the specimens is greatly accelerated too compared to that subjected to the single action of the sulfate attack. Under the condition of the double factors above, mineral additives decrease the resistance to sulfate attack, and the results have nothing to do with the C3S content in clinker.Seventhly, when cement based composite materials are subjected to the simultaneous action of the sulfate attack, external flexural stress and freezing-thawing cycles, the deterioration of the specimens is also greatly accelerated compared to that subjected to the single action of the sulfate attack. The higher the stress level reaches, the more quickly the specimens deteriorate. Under the condition of the triplicate factors above, mineral additives decrease the resistance to sulfate attack, and the results have nothing to do with the C3S content in clinker too. The mechanism of the multifactor synergetic damage is a result of microstructure to form and grow and theresistance to sulfate attack on cement based composite materials relates to its damage. Eighthly, the effectiveness of barium salts on suppressing the sulfate attack damage for cement based composite material is related to their types and contents. Barium hydroxide whose content is less than 1.0% replacement of cement by mass can suppress the sulfate attack damage for cement based composite material containing coal gangue. When barium hydroxide is added in the concrete, Ba2+ and SO42- can produce barium sulfate which can prevent AFt and gypsum crystal from forming. Sodium citrate has the same effect on suppressing the sulfate attack damage for cement based composite material containing coal gangue. The mechanism of suppressing the sulfate attack damage by sodium citrate is to reduce the content of Ca(OH)2 in pore solution finally to prevent AFt and gypsum crystal from forming.